We investigate the Dzyaloshinskii-Moriya interactions (DMIs) in perpendicularly magnetized thin films of Pt/Co/Pt and Pt/Co/Ir/Pt. To study the effective DMI, arising at either side of the ferromagnet, we use a fielddriven domain wall creep-based method. The use of only magnetic field removes the possibility of mixing with current-related effects such as spin Hall effect or Rashba field, as well as the complexity arising from lithographic patterning. Inserting an ultrathin layer of Ir at the top Co/Pt interface allows us to access the DMI contribution from the top Co/Pt interface. We show that the insertion of a thin Ir layer leads to reversal of the sign of the effective DMI acting on the sandwiched Co layer, and therefore continuously changes the domain wall structure from the right-to the left-handed Néel wall. The use of two DMI-active layers offers an efficient way of DMI tuning and enhancement in thin magnetic films. The comparison with an epitaxial Pt/Co/Pt multilayer sheds more light on the origin of DMI in polycrystalline Pt/Co/Pt films and demonstrates an exquisite sensitivity to the exact details of the atomic structure at the film interfaces.

Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We report on domain wall pinning behavior and the potential-energy landscapes created by notches of two different geometries in planar Permalloy nanowires. Domain wall depinning was probed experimentally using spatially resolved magneto-optical Kerr effect measurements. The spin structure of pinned domain walls was determined using Lorentz microscopy, and domain wall pinning behavior was also analyzed using micromagnetic simulations, which are in good qualitative agreement with experimental results. All notch structures have dimensions that are comparable with the domain wall length scales. For the notch structures investigated, the depinning field experienced by a domain wall is found to be relatively insensitive to notch geometry although the pinning behavior is highly sensitive to both the wall type and the wall chirality spin structure. Energetically, the notches present both potential barriers and/or potential wells depending on the micromagnetic structure of the domain wall, and we find that the chirality of the domain wall is a key determinant of the pinning potential landscape. The pinning behavior of domain walls is discussed in detail, and direct quantitative measurements of the width and depth of the potential wells and/or barriers responsible for domain wall pinning are given for vortex walls pinned in triangular and rectangular notches.

Continued development of GaN-based light emitting diodes is being hampered by constraints imposed by current non-native substrates. ZnO is a promising alternative substrate but it decomposes under the conditions used in conventional GaN metal organic vapor phase epitaxy ͑MOVPE͒. In this work, GaN was grown on ZnO / c-Al 2 O 3 using low temperature/pressure MOVPE with N 2 as a carrier and dimethylhydrazine as a N source. Characterization confirmed the epitaxial growth of GaN. The GaN was lifted-off the c-Al 2 O 3 by chemically etching away the ZnO underlayer. This approach opens up the way for bonding of the GaN onto a support of choice.

No abstract